Fluid catalytic cracking (FCC) processes are commonly used in refineries as a method for converting feedstocks to produce lower boiling fractions suitable for use as fuels. This can allow a variety of heavier feedstocks that are not directly suitable for lubricant base stock production to be converted into fuel boiling range fractions. Although FCC processes do not require hydrogen, a preliminary hydrotreatment step is often performed prior to FCC processing in order to improve the yield and/or product quality from an FCC process.
U.S. Pat. No. 3,929,617 describes a method to make a high quality UV stable lubricating oil stocks by hydrocracking a hydrocarbon feedstock under mild hydrocracking conditions to increase the viscosity index of the feedstock. The hydrocrackate product is subsequently solvent-extracted with a solvent having preferential solubility for aromatics, thereby forming extract and raffinate phases. The extract phase is stripped of solvent, and at least a portion of the substantially solvent-free extract phase is recycled to the hydrocracking step.
U.S. Pat. No. 4,213,845 taught a process to make lube oil stock with superior sunlight stability by blending 100 parts of raffinate with 10-45 parts of a raw hydrocrackate stock.